Tools' success metric is how much they make your task easier/faster. Ad delivery machines' success metric is how much of your time they waste.
Shitty UI making you spend more time in front of the screen is considered a good thing according to those "designers"' performance metrics.
For the last ~20 years: designing software for mobile devices
It's chock full of old screenshots from a variety of old desktops.
Microsoft’s desktop dominance was challenged by Google Docs and Facebook apps in parallel, Microsoft had to jump to web tech late, and the last few decades have been them reconciling their stack to the fact they missed the web and mobile despite pioneering key user-facing tech for both. Then they entered catchup-mode for client and search tech, only to later realize maybe they don’t care because the cloud catchup efforts blossoming into MS-consultant orthodoxy for every-darned-thing made their cloud offerings the most profitable bit… Ads and desktop stagnation pulled Windows into a weird OSX-at-home territory everyone kinda hates. And then LLMania took off, entrenching MS cloud and AI strategies into all of it, all the time. Pushing so hard that they’re gonna spend billions distancing their semi-Enterprise office brand from the term‘Microslop’.
TLDR: the rush to the web/mobile moved the focus off thick clients and desktop affordances, the money is elsewhere, a universal GUI toolkit isn’t obvious for anyone, and SaaS feels better online